Unusual reaction of N-aroyldihydrocyclopenta-pyrazolidinol with ketenes: formation of 1,3,4-oxadiazoles

Reaction of 3‐Formylchromone‐N‐benzoylhydrazone with Ketenes. Synthesis and Structural Studies of Chromone 1,3,4‐Oxadiazolines.

“…A proton transfer in the zwitterion from the neighboring NH group inactivates the ketene anion and the charge moves to the benzoyl oxygen with subsequent cyclization of the resulting dipolar intermediate 7 leading to the formation of oxadiazolines 3. An analogous mechanism was previously proposed by us for the reaction of ketenes with N-aroyldihydrocyclopenta-pyrazolidinol [13]. However, from the reaction of N,N-dialkylhydrazones with ketenes 2-azetidinone derivatives were isolated via a Staudinger [2+2] cycloaddition reaction, most probably because of the lack of the N-H moiety [14].…”

“…During the reaction time an amount of 3-formyl-N-benzoylhydrazone decomposed giving 3formyl-chromone 4 and benzohydrazide, which reacted further with ketenes to afford the corresponding Nbenzohydrazides 5a-5d in yields ranging from 3 to 20%. Structure Assignments The assigned molecular structures of all new compounds 3a-e are based on rigorous spectroscopic analysis including IR, NMR ( 1 H, 13 C, COSY H-H, NOESY H-H, HETCOR C-H and COLOC C-H), MS and elemental analysis data. In Tables 1 and 2 the NMR data [ 13 C, 1 H and the C-H correlation via one bond (HETCOR C-H) and two and/or three bonds (COLOC C-H)] are presented.…”

“…. White paper like solid in a yield of 40%, mp 231-233 ° (ethanol); ir (nujol) ν max : 1660, 1635, 1620, 1560 cm -1 ; 1 H, 13 C and COLOC nmr data are presented in Table 1; EIMS: m/z (%) 402/404/406 (8, M + ), 367/369 (24), 291 (100), 262 (5), 246 (96), 216 (30), 203 (90), 173 (98), 188 (13), 173 (98), 146 (53), 121 (75) 13 C nmr: δ 64.9 (C-11), 127.7 (C-2,6), 128.3 (C-3,5), 131.9 (C-1), 132.0 (C-4), 162.7 (C-10), 165.6 (C-7); EIMS: m/z (%) 246/248 (25, M + ), 213 (10), 163 (45), 121 (65).…”

“…2,3-Dihydro-3-isobutyryl)-2-(4-oxo-4H-chromen-3-yl)-5- phenyl-1,3,4-oxadiazole (3c). White paper like solid in a yield of 60%, mp 183-184 ° (ethanol); ir (nujol) ν max : 1660, 1635, 1620, 1560 cm -1 ; 1 H, 13 C and COLOC nmr data are presented in 11-H), 7.36-7.41 (m, 2H, (3,5)-H), 7.48-7.52 (m, 1H, 4-H), 7.81-7.84 (m, 2H, (2,6)-H), 9.58 (1 H, s, 8-H), 9.95 (1 H, s, 9-H). EIMS: m/z (%) 206 (100, M + ), 163 (15), 136 (95), 106 (100), 105 (95).…”

“…0.050 g. 5-phenyl-1,3,4-oxadiazole (3e). This compound was obtained as yellow solid in a yield of 49%, mp 188-190 ° (ethanol); ir (nujol) ν max : 1685, 1625 cm -1 ; 1 H, 13 C and COLOC nmr data are presented in Table 2; EIMS m/z (%) 426 (30, M + ), 333 (6), 321 (40), 319 (55), 305 (20), 291 (45), 290 (53), 280 (10), 262 (35), 248 (12), 230 (25), 216 (95), 205 (28), 188 (25), 173 (90), 172 (95), 146 (70), 131 (90), 121 (80), 120 (72), 108 (89), 107 (90), 106 (97), 105 (92), 103 (100). Anal.…”